The broad objectives of this proposal are to examine critically and in carefully controlled settings, the microbiologic and immunologic aspects of host defense in sudden infant death syndrome (SIDS). Specifically, it is hoped to 1) characterize mucosal immune system in SIDS and in appropriately matched non-SIDS control subjects, 2) determine the role of common respiratory viral infections in the etiology or pathogenesis of SIDS, and 3) initiate long-term epidemiologic, immunologic and clinical follow-up of infants with apneic spells and to define any association of these parameters in the event of sudden death in the infants.